1. Field of the Invention
The present invention pertains to a method for cleaning the cargo tanks of a marine crude oil tanker using a solvent to remove deposits such as waxes and asphaltenes which adhere to the cargo tank walls and floor.
2. Background
In the transportation of crude oil by marine tankers and the like, deposits of substances such as waxes and asphaltenes accumulate on the cargo tank walls and in the tank bottoms, in particular. These deposits require periodic removal by washing the tank surfaces with crude oil or hot water using apparatus which may be inserted into the tank from the tank top or deck of the ship. These devices are typically characterized by articulated jet nozzles which wash the tank walls with crude oil, hot water or other materials.
However, the interiors of the cargo tanks of marine tankers, in particular, are not simple cylindrical or four-walled chambers. The ship structural members such as deck girders, stringers, transverse frames, and other reinforcing members extend into the tank spaces and are coated with the same substances as the tank side walls and tank bottoms. Conventional tank cleaning practices do not sufficiently clean the surfaces of these structural members to the degree that is desired or necessary. During ship layup the tank interiors must be manually cleaned by workmen who are required to go into the tank with suitable cleaning equipment. If the tank surfaces have been neglected for too long a time, sand blasting may be required for a thorough cleaning. Both of these latter mentioned operations are expensive and time consuming.
Accordingly, there has been a need to develop a more convenient way of thoroughly cleaning the cargo tanks of marine tankers which does not interrupt operation of the ship and may, for example, be carried out during return transit of the ship to pick up a new cargo. The present invention is directed to a solution for the aforementioned problem in an efficient and uncomplicated manner.